1. Field of the Invention
The present invention relates to an integrated servo circuit which controls the spin motor and voice coil motor of a hard disk drive in response to digital commands generated by a microprocessor based controller chip.
2. Description of the Related Art
Most computer systems contain a massive memory storage device such as a hard disk drive. Hard disk drive units include a magnetic disk that is capable of storing a large amount of binary information. The magnetic disk is typically coupled to a hub that is rotated by an electric motor, commonly referred to as a spin motor. The drive unit also has a head that magnetizes and senses the magnetic field of the disk. The head is typically located at the end of a cantilevered actuator arm which can pivot about a bearing assembly mounted to the base plate of the disk drive. The actuator arm has a coil which cooperates with a magnet mounted to the base plate. Providing a current to the coil creates a torque on the arm and moves the head relative to the disk. The coil and magnet are commonly referred to as a voice coil motor or VCM. The actuator arm, motors and other components of a typical disk drive unit are relatively small and fragile, and are therefore susceptible to damage when subjected to excessive external shock loads or vibration. For this reason, hard disk drives are usually rigidly mounted to the housing of the computer system by screws or other fastening means.
Hard disk drives contain programs and other information that are vital to the user. It is sometimes desirable to transfer such information to a different computer system. Transferring programs from a hard disk typically requires loading the information onto a floppy disk, or sending such information over a phone line. Such methods can be time consuming, particularly if the program is long, or there is a large amount of data. There have been developed portable hard disk drives which can be plugged into a slot in the computer. To reduce the amount of possible component damage to the drive unit, the housing and disk assembly are constructed to be quite rugged. These rugged assemblies are typically heavy and bulky, and generally impractical to carry and store.
The Personal Computer Memory Card International Association (PCMCIA) has recently promulgated specifications for portable memory cards which can be plugged into slots within a computer. The PCMCIA standard includes a type I format, a type II format and a type III format, each format being distinguished by a different card thickness. Memory can be added to a computer by merely plugging in an additional card. Similarly, a modem or facsimile (FAX) card can be added to a system with the push of the hand. The standardized format of the cards allow a user to plug the memory card of one computer into another computer, regardless of the type or make of either system.
The standardized PCMCIA cards are approximately the size of a credit card and include a connector which mates with a corresponding connector in the computer. The small size of the card provides an electronic assembly that is easy to carry and store. It is very desirable to have a hard disk drive unit which conforms with the PCMCIA format, so that the disk drive can be readily carried and plugged into an existing slot of a computer. The existence of such a card would also allow the user to accumulate memory in the same manner that floppy disk are used today.
Hard disk drive units contain a number of integrated circuits that control the operation of the drive. The circuits typically include a read/write channel that is coupled to the transducers of the actuator arm assembly. The read/write channel is connected to an interface controller which is coupled to the host computer. The interface controller is coupled to a random access memory device that is used as a buffer to store data transferred between the disk and the host.
Disk drives also contain circuitry that provide current to the voice coil to maintain the head(s) on the center of a track (servo routine) and to move the head(s) from track to track (seek routine). Additionally, a disk drive typically contains circuitry to commutate the motor, and to insure that the motor and disk rotate at a uniform speed.
The operation of the above described circuits is typically controlled by a microprocessor based controller. Conventional disk drives also contain a separate circuit which provides an interface with the controller and the other circuits. This chip is commonly referred to as glue logic. U.S. Pat. No. 4,979,056 issued to Squires et al., discloses a hard disk architecture which has a microprocessor based controller that controls the operation of the interface controller, read/write channel, actuator and spin motor circuitry. The Squires system utilizes an embedded servo format which stores the servo information in the same sector of a track as the data. During each disk sector, the processor services the voice coil and spin motor circuitry of the drive. The processor employs a hierarchy that allows the spin motor and the voice coil to be serviced in conjunction with the transfer of data between the host computer and the disk. Although a Squires type system provides a controller based system that efficiently transfers data between the disk and the host, such systems typically require a large amount of electrical components that must be mounted onto a printed circuit board.
U.S. Pat. No. 4,933,785 issued to Morehouse et al. and U.S. Pat. No. 5,025,335 issued to Stefansky et al., disclose conventional hard disk drives which have a printed circuit board mounted to a disk drive housing commonly referred to as an HDA. The HDA is typically sealed and contains the disk, actuator arm and spin motor of the assembly. The HDA may also contain a pre-amplifier that is connected to the heads of the drive. The remaining electrical components (interface controller, read/write channel, actuator circuitry, etc.) are located on the printed circuit board, external to the HDA. The circuit boards of the Morehouse and Stefansky drive units extends along the entire length and width of the HDA. Therefore the thickness of the overall assembly is defined by the thickness of the HDA, the thickness of the printed circuit board and the height of the electrical components. It would be desirable to provide an architecture which would reduce the size of the printed circuit board, so that the board and accompanying chips do not add to the thickness of the assembly.